1. Field of the Invention
The present invention relates to an electron-emitting device, an electron source using the electron-emitting devices, and an image-forming apparatus using the electron source.
2. Related Background Art
The conventionally known electron-emitting devices are roughly classified under two types of thermionic-cathode and cold-cathode.
The cold-cathode include field emission type (hereinafter referred to as “FE type”) devices, metal/insulator/metal type (hereinafter referred to as “MIM type”) devices, surface conduction type electron-emitting devices, and so on.
Examples of the known FE type devices include those disclosed in W. P. Dyke & W. W. Dolan, “Field emission,” Advance in Electron Physics, 8, 89 (1956) or in C. A. Spindt, “Physical Properties of thin-film field emission cathodes with molybdenum cones,” J. Appl. Phys., 47, 5248 (1976), and so on.
Examples of the known MIM type devices include those disclosed in C. A. Mead, “Operation of Tunnel-Emission Devices,” J. Appl. Phys., 32, 646 (1961), and so on.
Examples of the surface conduction type electron-emitting devices include those disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965), and so on.
The surface conduction type electron-emitting devices utilize such a phenomenon that electron emission occurs when electric current is allowed to flow in parallel to the surface in a thin film of a small area formed on a substrate. Examples of the surface conduction type electron-emitting devices reported heretofore include those using a thin film of SnO2 by Elinson cited above and others, those using a thin film of Au [G. Ditmmer: “Thin Solid Films,” 9, 317 (1972)], those using a thin film of In2O3/SnO2 [M. Hartwell and C. G. Fonsted: “IEEE Trans. ED Conf.,” 519, (1975)], those using a thin film of carbon [Hisashi Araki et al.: Shinku (Vacuum), Vol. 26, No. 1, p 22 (1983)], and so on.
A typical device configuration of these surface conduction type electron-emitting devices is the device structure of M. Hartwell cited above, which is shown in FIG. 21. FIG. 21 is a schematic diagram. In the same drawing, numeral 1 designates an electrically insulative substrate. Numeral 4 denotes an electrically conductive, thin film, which is, for example, a thin film of a metallic oxide formed in an H-shaped pattern by sputtering and in which a linear electron-emitting region 5 is formed by energization operation called “forming” described hereinafter. In the drawing the gap L between the device electrodes is set to 0.5 to 1 mm and the width W to 0.1 mm.
In these conventional surface conduction type electron-emitting devices, it was common practice to preliminarily subject the conductive film 4 to the energization operation called the “forming”, prior to execution of electron emission, thereby forming the electron-emitting region 5. Namely, the forming is an operation for applying a dc voltage or a very slowly increasing voltage, for example at the increasing rate of about 1 V/min, to the both ends of the conductive film 4 to locally break, deform, or deteriorate the conductive film, thereby forming the electron-emitting region 5 in an electrically high resistance state. In the electron-emitting region 5 a fissure is formed in part of the conductive film 4 and electrons are emitted from near the fissure. The surface conduction type electron-emitting device experiencing the aforementioned forming operation is arranged so that electrons are emitted from the above-stated electron-emitting region 5 when the current flows in the device with application of the voltage to the above-described conductive film 4.
On the other hand, for example, as disclosed in Japanese Laid-open Patent Applications No. 07-235255, No. 08-007749, No. 08-102247, No. 08-273523, No. 09-102267, and Japanese Patent Publications No. 2836015, No. 2903295, etc., the device having experienced the forming is sometimes subjected to a treatment called an activation operation. The activation operation is a step by which significant change appears in the device current If and in the emission current Ie.
The activation step can be performed by applying a voltage to the device, as in the case of the forming operation, under an ambience containing an organic substance. This operation causes carbon or a carbon compound from the organic substance existing in the ambience to be deposited at least on the electron-emitting region of the device, so as to induce outstanding change in the device current If and in the emission current Ie, thereby achieving better electron emission characteristics.
FIG. 22 is a diagram to show a cross section of the electron-emitting device disclosed in Japanese Laid-open Patent Application No. 7-235255. In the same figure numerals 1, 4, and 5 are similar to those in FIG. 21, which are the insulating substrate, the conductive thin film, and the electron-emitting region, respectively. Numerals 2 and 3 denote the device electrodes for applying the voltage to the conductive film 4. The voltage is applied while keeping the electrode 2 at a lower potential and the electrode 3 at a higher potential. FIG. 22 shows the structure in which carbon or carbon compound 6 is deposited on the electron-emitting region 5 by execution of the aforementioned activation step, whereby the good electron emission characteristics are realized.
An image-forming apparatus can be constructed by using an electron source substrate having a plurality of such electron-emitting devices as described above and combining it with an image-forming member comprised of a fluorescent material and other members.